V-shaped defects in InxGa1−xAs/In0.52Al0.48As/InP pseudomorphic high electron mobility transistor structure

InxGa1−xAs/In0.52Al0.48As pseudomorphic high electron mobility transistor (P-HEMT) structures have been grown on semi-insulating InP substrates at two different growth temperatures of 520°C and 540°C by molecular beam epitaxy. The mobility of 9100 cm2 V−1 s with 2 dimensional electron gas (2DEG) carrier concentration of 5×1012 cm−2 and the photoluminescence (PL) peak at the energy of 0.87 eV have been achieved only in the sample grown at 520°C. The cross-sectional transmission electron microscopy (XTEM) investigation revealed the defects including slip with angle of 60 and 120° to surface for the sample grown at 540°C. Most of defects are formed with the shape of V and X and this resulted in upheaval of some internal areas. In this study the defects formation mechanism in the In0.52Al0.48As epilayers grown on InP substrate was explained by the difference in thermal expansion coefficients between In0.52Al0.48As epilayers and InP substrates. Also we proposed that the slip-like defects have been formed during cooling procedure and that slip-like defects in epilayer grown on the substrate temperature of 540°C only can be formed because it was higher than the optimum temperature for defect-free epilayers.